Battery Drain Estimator
Reads your battery level through the browser's Battery Status API, samples it every 30 seconds, and works out an observed drain rate.
Levels are coarse and the estimate only means something after several minutes of samples. Readings stay on your device; nothing is sent anywhere.
How it works
仕組みThis tool reads your device’s battery through the browser’s Battery Status API, then samples the level every 30 seconds to work out a real observed drain rate in percent per hour, alongside the operating system’s own time-to-empty estimate. Because drain depends on your screen brightness, your background apps, and your battery’s age, only a measurement taken on your own machine means anything; a generic spec-sheet figure cannot tell you how fast your laptop is draining right now. Leave the page open a few minutes for the estimate to settle.
Only Chromium browsers (Chrome, Edge, Opera) still ship the Battery Status API. Firefox removed it and Safari never shipped it, both citing fingerprinting concerns. On a desktop PC without a battery, Chrome reports a permanently full, charging battery instead.
Browsers report battery level in coarse steps, usually whole percent. Until the level actually ticks down between two samples there is nothing to measure, and a single 1% step over a couple of minutes gives a very rough rate. Ten or more minutes of samples gives a much steadier figure.
The operating system blends long-term discharge history with the current load, while this page only sees the minutes you have kept it open. If you just closed a heavy app or changed screen brightness, the two will diverge until your usage settles.